You might want to contact your local office of the American Automobile Association. There was no reason to register the car in California before taking it home. For all California knows, the owner of the car drove it to you!
For awhile California was charging out of state cars brought in. It was reversed and people got their money back.
Why all the complaints? The fact that you 0own a car is better than some. It is for the Collective good that you pay that tax. Maybe if you picked up poor people alongside the road and gave them free rides??? That would be more “fair”.
If CA is a state where the plates stay with the owner you’d have to go to the CA DMV to get a temp tag to drive it home.
Then they nail ya.
But ya, it does seem odd that he had to pay CA tax. I bought a salvage pickup from TX and had to pay sales tax on it even though it was shipped up here. When I called to ask why they said TX looks at salvage cars/trucks as “merchandise” and thus, is subject to state sales tax. I said, ok, but what about items shipped out of state? It was a trucking company that hauled it to Minnesota for me. Much like boxing the item up and sending it UPS..
Lost that fight too.